Background Opioid use and dosing for patients with chronic non‐cancer pain have dramatically increased over the past decade, resulting in a national epidemic of mortality associated with unintentional overdose, and increased risk of disability among injured workers. We assessed changes in opioid dosing patterns and opioid‐related mortality in the Washington State (WA) workers' compensation system following implementation of a specific WA opioid dosing guideline in April, 2007. Methods Using detailed computerized billing data from WA workers' compensation, we report overall prevalence of opioid prescriptions, average morphine‐equivalent dose (MED)/day, and proportion of workers on disability compensation receiving opioids and high‐dose (≥120 mg/day MED) opioids over the past decade. We also report the trend of unintentional opioid deaths during the same time period. Results Compared to before 2007, there has been a substantial decline in both the MED/day of long‐acting DEA Schedule II opioids (by 27%) and the proportion of workers on doses ≥120 md/day MED (by 35%). There was a 50% decrease from 2009 to 2010 in the number of deaths. Conclusions The introduction in WA of an opioid dosing guideline appears to be associated temporally with a decline in the mean dose for long‐acting opioids, percent of claimants receiving opioid doses ≥120 mg MED per day, and number of opioid‐related deaths among injured workers. Am. J. Ind. Med. 55:325–331, 2012. © 2011 Wiley Periodicals, Inc.